some lightspeed q's

[lyssword]

In big bang or gravitational expansion theory, I've heard that universe expanded faster than speed of light, and we only see 10% of universe as it is right now, is that true?

Another Q, if 2 particles run at each other @ speedoflight does it mean their collision will be faster than spl?

Thx

 

[Matthias99]

In big bang or gravitational expansion theory, I've heard that universe expanded faster than speed of light, and we only see 10% of universe as it is right now, is that true?

I've heard of some of this stuff, but I'm no expert. I think some of the theories are that c (the constant that is the rate of propogation of electromagnetic radiation in a vacuum, AKA the "speed of light") may have been higher early in the life of the universe than it is now.

Another Q, if 2 particles run at each other @ speedoflight does it mean their collision will be faster than spl?

First off, you cannot accelerate anything with mass to c. However, if you have two objects moving towards each other, and each has a velocity > 0.5c (from a 'neutral' non-moving observer's perspective), an observer will see the distance between them decreasing faster than c.

However, general relativity says that to an observer that is not 'neutral' -- say you're in a spaceship pacing one of the objects -- you will not observe that. You'll appear to be closing on the other object at a rate lower (but potentially very close to) c, and weird things like time dilation relative to the other object and neutral observer start happening instead.

 

[bobsmith1492]

If two objects approach each other, both moving at 0.95c from an outside observer, they are only approaching each other at something like 0.99c from their frame of reference; it all depends on your frame of reference, but from no frame of reference can anything move or appear to move faster than c (except maybe tachyons or exotic negative-mass particles that are only theoretical anyway...). Hm, I just said frame of reference way too many times for this frame of reference. Dah!

 

[f95toli]

Originally posted by: lyssword
In big bang or gravitational expansion theory, I've heard that universe expanded faster than speed of light, and we only see 10% of universe as it is right now, is that true?

As far as I understand it is possible, nothing WITHIN our universe can travel faster than c, but AFAIK there is no reason why the universe itself can not expand at a rate where the difference between different parts increases at a speed larger than c.
This would as you say also imply that there are regions of the universe that we can never know about since a signal would need to travel at a speed larger than c in order to carry that information.

 

[NikolaeVarius]

I think nothing can travel faster then the speed of light relative to anything else. The universe expanded unrelativiley which is why its possible for it to expand faster than light.